White House National Security Adviser Jake Sullivan says US President Joe Biden is "prepared to go to the table to talk to the Iranians about how we get strict constraints back on their nuclear program".

"That offer still stands, because we believe diplomacy is the best way to do it," Sullivan told CBS News on Sunday.

"Iran has not yet responded. But what's happened as a result is that the script has been flipped it is Iran that is isolated now diplomatically not the United States and the ball is in their court."

Last week, Washington said the US was was prepared to re-engage in diplomacy, raising hopes for a revival of the badly damaged accord.

The nuclear deal was reached in 2015 in an effort to prevent Iran from being able to produce nuclear weapons, lifting sanctions in exchange for Iran limiting itself to civilian nuclear applications.

But Biden's predecessor Donald Trump pulled out of the agreement in 2018, arguing that it did not do enough to stop Iran from being a regional troublemaker, and since then, Iran has slowly backed out of the deal.

The new US administration wants to come back to the treaty if Iran adheres to its obligations again.

However, Tehran on Sunday said it wants Washington to take the first step by lifting sanctions, which have led to the worst economic crisis in Iran's history, in particular sanctions on vital oil exports.

Australian Associated Press